It's said that tabletop RPGs are limitless. That's not true. It's been over 40 years now. We know better. There are limits to what you can do with a tabletop RPG, and a lot of those limits have to do with what players are willing to play. This is a conceptual limit, and I call it "playable space".
I touched on this when I wrote about Palladium Books losing the Robotech license (again). The reason for why tabletop RPGs based on mecha properties fail so often is because the playable space is already firmly addressed--filled--by tabletop wargames and their videogame counterparts. Players don't want to NOT play mech pilots. They want to smash giant robots together and not mess with all the drama-llama bullshit that so often goes on around the giant robot combat.
Other perennial failures are explained in this fashion. You don't get successful games based on starship crews because the fantasy is not being the bitch trying to put out fires, or Scotty his way around ship damage. It's to be the shot-caller, the captain or admiral, and the rest of the crew really doesn't matter- they are not viable PCs. Yes, even in Firefly (i.e. Traveller) games.
The same goes for a lot of popular character ensembles when translated to tabletop RPGs. The reason is that players are there to play the game, and that doesn't mean being someone's bitch (The Cleric Problem) or being sidelined most of the time because they have sweet fuck-all to do with what's going on. (The Decker Problem) In short, what can work in fiction doesn't in gaming more often than not; Relena Peacecraft isn't playing the same game as Heero Yui, and it's long past time for tabletop game designers (most of whom really ought to know better- looking at you, Everyone That's Been Getting Paid For This Since 1990) to recognize this openly and build their products accordingly.
The same goes for the Game Masters. You need to know what game you're running, and then go through your ruleset and ruthlessly cull every last little thing that doesn't belong. Character options, rules, content, everything. Players want the game to Just Fucking Work. They will never do homework; if it isn't at the table during play, it won't be done. Learn from Sisyphus and stop trying to push that boulder uphill. That dog doesn't hunt; stop trying.
The core of the medium is that of a skirmish-scale wargame, focused on the location of desired resources and using them to facilitate the upgrading of player avatars. That's Dungeons & Dragons as it is, stripped of all pretension and other obfuscating bullshit. It is no surprise that failures in this medium are those that don't work with this model of gameplay; it's also no surprise that successes adhere to it, or define their own paradigm of play that then gets adhered to (e.g. Call of Cthulhu).
Which leads to another limitation: commercial viability.
Gamers wants to play games. "RPGs" that have no game are going to fail, and have to be propped up by endless gimmick bullshit (including retards virtue-signalling and stunt-casting live-streamed promo games) instead because real gamers don't play fake games- only fake gamers pretend to play fake games.
And the tabletop RPG field is filled with the corpses of commercial failures that died due to a lack of viability. Many of these are Fantasy Heartbreakers (Not-D&Ds with often just one gimmick to make them stand apart), and many more are mis-applied licensed games (such as Robotech), because those publishing the games grossly over-estimated the customer base for that thing.
In short, Most Gamers Want D&D if they want a tabletop RPG. The best not-D&Ds either stake out their own turf (CoC) or apply the formula to a not-Pink Slime Fantasy niche before D&D got there. The result is that all of the playable spaces are now staked out and there's actually no room left for expansion- only for usurping someone already lording over a domain. Furthermore, videogame tech keeps eating away at the competitive advantages of tabletop RPGs from one end while boardgames do so from the other, and those same folks who ought to know better still refuse to deal with reality as it is and unfuck their offerings. (Especially WOTC and Paizo.)
Because they still think tabletop RPGs are limitless, in the face of all this contrary evidence, and engaging in delusional behavior that makes Don Quixote look on in horror and say "They're all mad, Sancho. They think those giants are actually dragons!"
And people wonder why I don't care if the entire tabletop RPG business collapses. It should. Heed the Wisdom of Harry Callahan: